The IP Multicast service model extends the traditional best effort Internet datagram delivery service for efficient multi-point packet delivery. However, in spite of a decade of research on multicast protocols and applications, a globally deployed multicast service is nowhere in sight, hindered by multitudes of problems such as manageability, lack of a robust inter-domain multicast routing protocol, scalability, and heterogeneity. In this work, we propose a new model for Internet multicast where we view multi-point delivery not as a network primitive but rather as an application-level infrastructure service. Our architecture relies on a collection of strategically placed network agents that collaboratively provides the multicast service for a session. Clients locate a nearby agent and tap into the session via that agent. Agents organize themselves into an overlay network of unicast connections and build data distribution trees on top of this overlay structure. This model effectively pa...